It is estimated that 10-30% of fertilized human eggs are aneuploid. Most of these aneuploid fertilizations result in either embryo demise prior to clinical recognition of pregnancy, or miscarriages. Aneuploidy is also the single most important contributing factor in severe birth defects (e.g. Down syndrome). The majority (>80%) of embryo aneuploidies are of maternal origin (eggs having incorrect number of chromosomes), with majority being due to premature separation of sister chromatids (PSSC) immediately prior to ovulation. Advanced maternal age is the most important contributing factor of aneuploidy, with women over 32 having a rapidly increasing risk of carrying a trisomy pregnancy, where the risk reaches over 30% by age 40 (Hassold and Hunt, 2001).
In order to avoid aneuploid pregnancies, women undergoing in vitro fertilization (IVF) may undertake pre-implantation genetic diagnosis (PIGD), which involves polar body or embryo biopsy. This procedure is invasive and therefore inherently harmful to the implanting embryos. Overall, the benefit is not universally recognized. Several major public health authorities have issued strong warnings against its use, and it is prohibited in some countries (for example, Germany).
It is, therefore, desirable to provide a way to reduce the risk of having an aneuploid pregnancy.